#28 fix setup to allow build with the system qhull

[Frédéric PICCA]

Hello Armando,

here my proposition of patch to fix the build system and use the qhull library if available.

the user need toprovide the relevant information via the

QHULL_CFLAGS ans QHULL_LIBS environement variable.

exemple

export QHULL_CFLAGS=-I/usr/include/qhull
export QHULL_LIBS=-lqhull

if one of the variable is missing, the system faullback to the embeded version.

cheers

fred

[V. Armando Sole]

Patch implemented.